Ajay K. Sood
Department of Entomology, CSK Himachal Pradesh Krishi Vishvavidyalaya, Palampur (H.P.)
Email: firstname.lastname@example.org; email@example.com
The warm, humid conditions and abundant food under protected conditions provide an excellent, stable environment for pest development. Often, the natural enemies that keep pests under control outside are not present under protected environment. For these reasons, pest situations often develop in the indoor environment more rapidly and with greater severity than outdoors. The damage inflicted by arthropod pests on greenhouse crops varies with the pest and season. The level of damage that can be tolerated is greatly dependent on the type of crop. Producers of vegetable crops generally can accept a higher level of damage than those of ornamental crops that are produced for their aesthetic value.
Integrated pest management (IPM) is a systematic approach to manage pests that combines a variety of techniques and strategies to either reduce pest populations or lessen their economic impact. It is a site-specific strategy for managing pests that relies on correct pest identification and understanding the pest biology. With a long-term perspective it is easier to see that an investment in IPM can pay for itself in a higher-quality crop and a cleaner environment.
Insects and Mite Pests under Protected Environment
The growing conditions within the protected environment of greenhouse/ polyhouse are highly favourable to arthropod pests. In India, about twenty insect and mite species have been recorded to be associated with the crops under protected environment. Some of the important pest groups are aphids (Myzus persicae, Aphis gossypii), caterpillars (Spodoptera spp., Helicoverpa armigera), leafminer (Liriomyza trifoli), mites (Tetranychus urticae and Polyphagotarsonemus latus), thrips (Thrips tabaci and Scritothrips dorsalis) and whiteflies (Trialeurodes vaporariorum and Bemisia tabaci). The detailed account of the insect-pests associated with crops under protected environment is being presented in Table 1.
Table 1. Insect-pests Scenario under Protected Environment in India
Insect and mite pests
Capsicum, tomato, carnation
Punjab, Uttrakhand, H.P.
Rose, tomato, capsicum, cucumber
Karnataka, Punjab, HP
Tomato, cucumber, chrysanthemum, gerbera, and many ornamentals
Polyphagotarsonemus latus (yellow mite)
Karnataka, Punjab, Delhi, H.P.
Tetranychus urticae (Spider mite)
Tomato, capsicum, cucumber, carnation, gerbera
Tomato, cucumber, capsicum, beans, gerbera, and more than 30 hosts
H.P.and Nilgiri hills (TN)
Each crop has a set of typical pests that attacks under certain conditions. This information should be available with the grower to aid in diagnosis and to help understand the life cycle of the pest. Correct identification is critical to selection of appropriate management tactics, because individual species can display different susceptibilities to chemical and other measures.
Aphids or plant lice are small, soft-bodied, sedentary insects that form colonies on the leaves and stems of the host plants. They suck the cell sap from leaf or apical growing parts and prefer to feed on tender, young growth. Aphids multiply at rapid pace completing one generation in 7-10 days. They give birth to six to ten young ones per day with 50-100 in total life span. Thus, enormous populations can build up in a relatively short period.
Feeding by aphids can cause leaves or stems to curl or pucker. This leaf distortion often protects the aphids from contact insecticides. They also secrete honeydew on which black sooty mold develop in the periods of high atmospheric relative humidity which interferes with photosynthetic activity. They also act as vector of many viral diseases.
Two species of caterpillars are associated with the crops under protected environment. These are tobacco caterpillar (S. litura) and tomato fruit-borer (H. armigera).
Tobacco caterpillar: The fore wings of adult moths have beautiful grayish brown pattern with grey wavy lines. A single female lays about 300 eggs in clusters covered by brown hair. The full fed larva, upto 5 cm in length, is velvety black with yellowish green dorsal stripes and lateral white bands. They pupate in soil.
They are mainly foliage feeders, but occasionally damage fruits. Eggs are deposited by female moths that have made their way into the greenhouse and lay eggs in large masses. Heavy infestations may occur in isolated areas within the greenhouse, and timely spot treatments can often provide effective control.
Tomato fruit-borer: Tomato fruit-borer is one of the most significant insect-pests of field-grown crops. They are less common in greenhouses, but when infestations do occur, they can cause serious losses. This is because, as their name implies, this caterpillar feeds directly on the fruit. This insect attacks many other crops. These are stout bodied, green or brown striped caterpillars about 3-4 cm long when fully grown. The moths are light brown with a small brown spot on each forewing.
Tomato fruit borer feed on blooms, as well as immature and fruits. The individually laid eggs are most often deposited on leaves near upper bloom clusters. If not controlled, heavy infestations of these caterpillars can destroy the crop. Because large larvae that have already bored into fruit are very difficult to control, it is important to detect infestations and begin treatment when caterpillars are small.
Eggs hatch within 3 to 7 days, depending on species and temperature. The small caterpillars begin feeding on leaf tissue. The caterpillar stage lasts about 11 to 17 days with larvae eating more and causing proportionally more damage as they become larger. Upon completion of its larval development the caterpillar transforms to a pupa on the foliage or in the soil, depending on species. Moths may emerge from these pupae in 7 to 11 days.
Leafminers are larvae of small flies. They damage plants by feeding between the upper and lower surface of the leaf by forming mines. The mines increase in width as the larva grows. When fully grown, the larva emerges from the leaf and fall to the ground to pupate. Each female fly lays 50 to 100 eggs by making punctures in the leaf tissue.
Damage is caused by larvae mining the leaves. If the infestation is severe, photosynthetic activity is reduced affecting plant vigour. Because the damaging stages of the insects occur entirely inside the leaf, control with contact insecticides is ineffective once the damage appears. Infestations can be avoided through the use of good cultural practices, hand romoval and disposal of infested leaves and use of chemical controls when necessary.
Mites are sap-sucking pests which attack a wide range of greenhouse plants. Two species, the two-spotted spider mite (T. urticae) and the yellow mite (P. latus), are known to be persistent problems. These mites feed by piercing tissue with their mouthparts and sucking out cell contents.
Two-spotted spider mites are light to dark green with two distinctive black spots on the abdomen. Eggs are spherical and clear when laid. After hatching, the larva has three pairs of legs, but later stages have four pairs and are known as proto- and deuto-nymphs. Heavy infestations of the two-spotted spider mite produce fine webbing which may cover the entire plant. Generally they feed on the undersides of leaves, giving the upper leaf surface a speckled or mottled appearance. Leaves of mite-infested plants may turn yellow and dry up, and plants may lose vigour and die when infestations are severe. Females can lay 100 to 150 eggs, and during hot, dry weather the life cycle may be completed in seven days. The pest can complete upto 30 generations in a year. In the extreme winters the females are reported to overwinter in the plant debris and cracks and crevices.
Yellow mites are minute, elliptical, semi-transparent, greenish mites. These mites thrive when the temperature is mild with humid environment and can complete their life cycle in about two weeks. Depending on the type of plant attacked, they may infest the entire plant or be concentrated around the buds. Infested leaves become distorted and often curl inward; foliage may become darker than that of healthy leaves. Because of their small size, infestations often go undetected until the damage is severe. Usually it is the nature of the injury, not the mites themselves, that alerts greenhouse managers to yellow mite infestations. Often, it is better to discard infested plants or parts than to attempt to control the problem with pesticides.
Thrips are tiny, slender insects about 1-1.5 mm long. They range in color from light brown to black. They have four wings, each fringed with a row of long hairs that are held flat over their back. Female thrips insert eggs into slits in the tissue. Eggs hatch in two to seven days. Nymphs feed much like adults and molt four times during development. They pupate in debris or soil. Winged adults are carried into the greenhouse on contaminated plant material, or they fly in.
Thrips infest the leaves, flowers, buds and young fruits of a crop. They feed by rasping the plant surface and sucking up the exuding sap. Heavily infested leaves have a mottled or silvery appearance.
Whiteflies are serious pests in the greenhouse. Two species of whiteflies are prevalent under protected environment namely, greenhouse whitefly (T. vaporariorum) and cotton whitefly (B. tabaci). The former is prevalent in temperate regions whereas the other is a serious pest in tropical and sub-tropical parts of the country.
Whiteflies are small snowy white in colours, about 2 mm in length, flutter from the undersides of leaves when the plants are disturbed. The lower surface of the leaves is infested with all life stages of whiteflies. The female of these sap-sucking insects may lay upto 150 eggs at the rate of 25 per day. The entire life cycle takes 21-36 days, depending on the greenhouse environment. They can complete more than 12 generations in a year.
Both the nymphs and adults of whitefly feed on phloem cell sap and causes chlorotic spots. The leaves dry-up prematurely and plant growth is affected. Nymphs also secrete a sticky substance known as honeydew, which covers leaf surfaces and flowers on which the sooty growth takes place under humid weather conditions.
Since greenhouse conditions allow rapid development of pest populations, successful control of insect pests on greenhouse vegetables and ornamentals depends on several factors. The IPM programme for protected cultivation can be described as a pyramid constructed having three key components namely, Avoidance of problem; Sampling and early detection; and Curative measures.
With "Avoidance" as the foundation, virtually all the non-curative preventive management components (e.g. physical, mechanical and cultural means) can be fitted. Confronted with a pest crisis, short-term function depends on the upper two levels of the pyramid. However, sustainable, long-term strategies must depend on the development of this solid foundation. At the same time, a pyramid-strategy developed for one pest must be compatible with like strategies in place for all pests of a system.
Although physical and cultural measures do not have a curative effect after heavy infestations of greenhouse pests, their preventive and delaying effect on the rapid increase of pests is of great importance in integrated pest management.
1.1 Use of Physical Barriers
1.1.1 Use of Insect-proof screens
One strategy particularly suited to greenhouse IPM programmes is the use of physical barriers to exclude insect-pests. Screening removes an important variable from a grower's pest management program - the movement of pests into the greenhouse from outside. This includes common greenhouse pests such as thrips, aphids, leafminers and whiteflies, but also some less common pests such as fruit borers. Screening vents and doorways can greatly limit the movement of insect pests into the greenhouse. However, selection of proper screen size mesh and assuring adequate airflow are more important.
Mesh size depends upon the targeted insect (Table 2). Mesh with holes less than 200 micrometers is required for complete exclusion of thrips; however, screening with holes as large as 600 micrometers is sufficient for excluding leaf miners.
Table 2. Screen mesh sizes needed to exclude major greenhouse pest species
Hole size (micron)
Mesh (Number of threads per linear inch)
Leafminer (L. trifoli)
Cotton whitefly (B. tabaci)
Aphid (M. persicae)
Greenhouse whitefly (T. vaporariorum)
Thrips (Thrips spp.)
For the exclusion of thrips a screen mesh of 76 is required. Obviously, screening that keeps out thrips also keeps out larger pests, such as aphids and whiteflies. However, selection of screen with particular mesh size is site specific and depends on the prevalent pests of the crop in the locality. The smaller the holes in the mesh, the more reduction there will be in airflow. This reduction can be counteracted by increasing the surface area through which air flows. Screening can be stretched from gutter to gutter to increase surface area.
1.1.2 Provision of double door
Limited access to screened areas is beneficial since insects may come in the protected structure on clothing or be swept in with the wind. Building a screened foyer to create a double-door entry partially solve the problem of wind-carried insects. Special efforts must be put in for repairing holes or tears immediately, and cleaning the screens to maintain airflow.
1.1.3 Ultra-violet radiation absorbing sheets
Altering the visual behaviour of insects has been used successfully as a tool in IPM programmes directed to protect crops from insects and insect-borne viral diseases. The first evidence that UV-absorbing films may reduce insect invasion of greenhouses came from Japan.
Insects perceive light signals through their compound eyes. The anatomy and physiology of the compound eye is adapted to sense UV wavelengths alone or a mixture of UV and visible radiation. The UV part of the solar spectrum plays an important role in the ecological behavior of insects, including orientation, navigation, feeding and interaction between the sexes.
Spectrally modified sheets are produced commercially by the introduction of a UV-absorbing additive into the raw material which blocks the transmission of most wavelengths in the UV range below 370-380 nm without interfering with the transmission of photosynthetically active radiation (400-700 nm).
The manipulation of the UV vision of insects by using UV-blocking greenhouse cladding materials has been shown to be effective in preventing the immigration of a wide range of insect-pests (whiteflies, aphids, thrips and leafminers) from the external environment into the protected crop. It was found that populations of aphid (A. gossypii), greenhouse whitefly (T. vaporariorum), thrips (Frankliniella occidentales and Scirtothrips dorsalis) and leafminer (Liriomyza sp.) were lower on tomatoes grown in a plastic-house made of polyethylene treated to exclude UV wavelengths than on crops grown in an ordinary plastic house. The number of whiteflies, aphids and thrips trapped on sticky yellow cards under a UV-absorbing film were 10 - 100 times lower than the number trapped under regular films. The use of UV-A films also helped in reducing the number of insecticide applications by 50-80% for the management of Spodoptera lituralis.
1.2 Sanitation and Cultural Practices
Many of the methods incorporated in an IPM strategy are logical greenhouse operating procedures and basic horticultural practices. The following methods produce a healthier crop, prevent many pest problems, and isolate pests to smaller areas in the greenhouse. Some of the important one is:
1.2.1 Pre-season cleanup
A basic component of cultural practices is sanitation. Infestations are easier to prevent than to cure. It has been observed that insects can enter the protected structure in following three ways:
- Introduction of infested seedlings/ planting material
- Infestation from other plants within the protected structure
- Infestation from host plants outside but near the protected structures
Before introducing a new crop into the greenhouse, it is extremely important to eliminate pests from the previous crop. Remove all plant debris and weeds from the greenhouse. Many pests also occur on other crops or broadleaf weeds. For this reason, it is important to avoid growing other crops next to the greenhouse and to prevent heavy growths of broadleaf weeds around the outside edges of the greenhouse. Under protected environment monoculture is suggested, however, if one has to go for polyculture then avoid staggered planting.
A fallow period of two to four weeks reduces the pest load considerably. To determine the presence of thrips, whiteflies, leafminers, or other insects, set up yellow sticky cards and indicator plants after watering. Observe for any insects that are trapped on the cards after two days and continue till the activity is ceased and only thereafter the decision regarding plantation of new crop be made.
One of the most important points in protected cultivation is to begin with insect-free planting material. When new plants arrive at the greenhouse, examine them closely for signs of pest infestation. If necessary, remove lower or damaged leaves to avoid spread of pests. Make the decision whether treatment is needed from the first sign of symptoms of insects or mites. It is much easier to manage a pest infestation by treating a group of small plants (in seedling stage) rather than larger plants where the dense canopy prevents thorough coverage.
1.2.3 Balanced use of fertilizer
Fertilization schedules based on balanced use of nutrients should be followed. Nitrogen should be applied only as needed for optimal growth. Periodic heavy applications set up nitrogen surpluses that cause excessive growth, which favour the population growth of aphids, and other pests. Application of potassium at desired levels has been found to reduce the incidence of insect-pests.
1.2.4 Pinching and Pruning
Pinching-off damaged plant parts, flowers, and spotted leaves (and those with insect larvae or egg deposits) can be a very effective way of reducing the spread of pests in the greenhouse. The plant debris should be placed immediately in a covered container before being disposed-off. This practice can be helpful in reducing the pest population of all the targeted pests.
Pruning lower leaves after harvesting lower fruit clusters is helpful measure in removing large numbers of developing leafminers and whiteflies.
2.5 Plant Quarantine
Workers in the greenhouse are frequently the mechanism for dispersal of insects and mite pests. One should try to avoid moving plants with mites or thrips and they should not be touched or moved immediately before handling clean, healthy plants.
2.6 Trap crop/Indicator plants
For early detection and trapping of the target pests, some of the preferred hosts of the target pests can be used. Planting border rows of Portulaca oleracea in rose can be used as a trap crop for tobacco caterpillar under protected environment.
2. EARLY DETECTION
Scouting and early detection are critical to manage the insect infestation successfully. Monitoring or scouting is the regular, systematic inspection of the plants and exteriors to identify and assess pest problems. It includes inspection of foliage and flowers; and the use of insect traps. Many insect infestations begin in isolated spots within the greenhouse. Timely crop monitoring identifies situations where pests are absent or are at levels well below those necessary to cause damage, thus preventing unnecessary control applications and expenditures
Scouting procedures for most greenhouse-grown crops are based on visual observations and are used to provide estimates of the pest population in protected environment. The common pests that attack greenhouse crops do not distribute themselves evenly throughout the crop. Therefore, it is imperative to scout the entire greenhouse in a consistent, uniform pattern. Inspect the entire plant, including the soil surface, for the presence of arthropod pests. Look at the plant systematically each time. Begin at the bottom and work up. Look at the older leaves, the young, tender leaves, and the flush growth. When the crop is young, it is important to check all the leaves on the plant. Because a majority of arthropod pests associated prefer the underside of a leaf, it is important to turn the leaves over to check for pests. The detailed account of observations to be recorded is presented in Table 3.
Scout the crop on a regular basis and at least 1-2% of the total plants should be inspected at weekly interval. A thorough greenhouse inspection reveals the location and severity of any current pest problems. One should use a field data sheet to record the identification, location, and severity of all pests present, and record the effectiveness of any treatments.
It is a relative method of insect population estimation where no direct observations on the plants for the presence of insect-pests are needed. However, the pest population is estimated with the help of attractant traps. For whiteflies, aphids, thrips and leafminer adults, yellow sticky cards (4″x12″ or 8″x12″) are an excellent supplement to pest observation in the protected environment. Additionally, for thrips blue coloured sticky traps can also be used. Though the sticky traps are available commercially, however, they can also be fabricated indigenously at growers level by using pieces of fluorescent yellow chart paper and pasting castor oil/ mustard oil or the commercial grade adhesive, the polybutene, on both the surfaces. The traps are placed in a grid pattern and 1-2 yellow sticky cards per 100 square meter of floor area are used. If the target is mass trapping, then number of traps can be increase to five or more. Hang the yellow sticky cards/ traps in the crop with the help of strings about 4″ to 6″ above the plant canopy. As the crop grows, cards can be moved up. Designate the location of each sticky card on a map of the greenhouse. Check the sticky cards every scouting visit (twice a week if possible) and record the total number of whiteflies, thrips, winged aphids, and leafminer flies from each card on the field data sheet. Change the cards when more than 60-70% of the area is covered by trapped insect.
Apart from this, sex pheromone baited traps can also be used for detecting moths of tobacco caterpillar and tomato fruit borer. These traps allow visualizing population trends and can be used to time the application of pesticides or release of bioagents. The detail of the scouting and monitoring plan is given in Table 3.
Table 3. Monitoring and scouting technique for pests under protected environment
Inspect underside of leaf
Inspect upper surface for stippling/ small white spots
Inspect leaves for mines within tissue
Inspect new growth or terminal for feeding
Tap flowers over white surface & look for movement
Press lower leaf surface on white card and look for spots on cards
Honeydew or sooty mold
Small black spots on leaves (fecal drops)
Holes/ skeletonized spot in/ on leaves
Frass on leaves
Small black spots on leaves (faecal drops)
Chlorotic (yellow) spots on upper leaf surface
Casted-off skins on leaf
Curling of leaves
Distortion of new growth
Buds fail to open or uneven opening of flowers
Webbing on leaves/ flowers
Yellow sticky card at top of plant canopy
Blue sticky card at top of plant canopy
3. CURATIVE MEASURES
3.1 Biological Control
Practically every crop pest has its natural enemies in the form of parasitoids or predators. The biological control involves a large scale multiplication and liberation of such agents, or creating conditions under which the naturally occurring agents can act effectively. In field situations, some very outstanding successes have been achieved by using biocontrol agents, but the method suffered a set-back owing to the large-scale and indiscriminate use of insecticides.
Use of specific predators and parasitoids in greenhouse ecosystem to manage pests forms the basics of biological control. But to be effective, biological control must be well planned and begun when the target populations are low. In Western Europe and North America, the bioagents are commercially available and being used successfully for the management of pest problems under protected situations (Table 4).
Table 4. Registered natural enemies for pest management in protected cultivation in Europe and United States
Serpentine leaf miner
Phytoseiulus longipes Phytoseiulus persimilis
insects and eggs
insects and eggs
However, under Indian conditions this technique though is having potential but have following limitations
- Temperature extremes and the effect of chemical pesticides affecting the capabilities of natural enemies.
- Low tolerance of pest damage amongst consumers especially in ornamentals
- Lack of a system for supplying natural enemies of good quality
3.2 Chemical Control
The insecticides are curative in action and are one of the important tools to check the flaring pest populations. Insecticides belonging to different groups namely, botanicals pesticides, microbial pesticides, Insect Growth Regulators (IGR), synthetic chemical pesticides etc. are in use. Some of the serious limitations of the insecticides have been highlighted in recent years. Out of these, the problems of insecticides residues on crops have been agitating the minds of people in developed and developing countries of the world due to indiscriminate use of pesticides. However, the sensible approach suggested and generally accepted is for need based judicious and safe use of insecticides.
Under protected environment, in order to avoid the contamination of produce from pesticide residues, use of pesticides having less persistence and adopting suggested waiting period between last insecticidal application and harvesting can be followed.
Other challenge with pest managers is to minimize the development of resistance in pest species to the pesticides. This can be checked or delayed by avoiding repeated application of same insecticide and also from same group. Incorporating botanicals, microbials and others in management schedule proves better in Insecticide Resistance Management Programme (IRM).
Apart from this, the safety of the pesticide applicator should also be taken into consideration as the chemical pesticides become more volatile under high temperature regimes of the protected environment. One should apply the pesticides by taking all safety measures including the protective kit to avoid the direct effect of pesticides to the applicator. A re-entry period of atleast 12 hr should be observed after application of pesticides. Insecticides with fumigant action need to be avoided under protected structures.
Research efforts are needed for developing pest management technology under protected environment with emphasis on avoidance and selective use of pesticides. Safe waiting intervals based on harvest time pesticide residues needed to be established for the crops under protected environment as this information is lacking completely. Apart from this, emphasis to improve the awareness level of the growers for timely diagnosis and judicious use of insecticides needs to be taken up on priority.
Submitted by ajaysood on Tue, 21/09/2010 - 13:31